1. Field of the Invention
The present invention relates to a shadow mask for cathode ray tubes (CRTS), and, more particularly, to a shadow mask for cathode ray tubes having slots whose shapes are optimized to prevent interference between the slots and an electron beam, which may occur in wide-angle slim-type cathode ray tubes.
2. Description of the Related Art
FIG. 1 is a side view, partially in section, showing the inner structure of a conventional cathode ray tube.
As shown in FIG. 1, the conventional cathode ray tube comprises a panel 1, a funnel 2, a shadow mask 3, a screen 4, a frame 5, a spring 6, an inner shield 7, a deflection yoke 8, an electron gun 9, and a reinforcing band 10.
The conventional cathode ray tube is operated as follows: an electron beam emitted from the electron gun 9 is vertically and horizontally deflected by the deflection yoke 8, which is disposed at a neck part of the funnel 2, and then arrives at the screen 4, i.e., a fluorescent surface applied to the inner surface of the panel 1, through slots formed at the shadow mask 3. At this time, the screen 4 emits light by energy of the electron beam such that a picture is reproduced, and therefore, a user can watch the picture reproduced through the panel 1.
Generally, the shadow mask 3 is supported while the shadow mask 3 is in parallel with the panel 1. To this end, the frame 5 of the cathode ray tube is fixed to one side of the shadow mask by welding. Also, the spring is disposed between the frame 5 and the panel 1 for securely connecting the frame 5 to the panel 1.
The inner shield 7 of the cathode ray tube intercepts terrestrial magnetism to prevent the path along which the electron beam moves from being curved by the terrestrial magnetism. Also, the reinforcing band 10 is attached to the cathode ray tube for dispersing stress applied to the panel 1.
The cathode ray tube has a total length greater than those of the other display units, such as a liquid crystal display (LCD) or a plasma display panel (PDP), which results from its picture reproduction method. For this reason, various efforts have been made recently to slim the cathode ray tube. This is because that slimness of the cathode ray tube considerably strengthens the competitiveness of the cathode ray tube.
The slimmed cathode ray tube has a decreased total length. As a result, the deflection angle of the electron beam is increased. When the deflection angle of the electron beam is increased, interference occurs between the electron beam and the shadow mask, which will be described below in detail with reference to FIG. 2.
FIG. 2 is a view showing paths along which the electron beam passes through a slot 3a of the shadow mask 3.
In the case of the conventional cathode ray tube, the deflection angle between catercornered ends of the effective surface of the panel from the center of deflection is approximately 90 degrees to 110 degrees. In the case of the wide-angle slim-type cathode ray tube having a total length of 35 cm or less, on the other hand, the center of deflection is shifted toward the panel as a result of the reduction of the total length, and therefore, the deflection angle is increased up to 120 degrees or more.
One of the paths shown in FIG. 2 is a path along which the electron beam passes through the slot 3a formed at the shadow mask 3 in the conventional cathode ray tube, and the other path shown in FIG. 2 is a path along which the electron beam passes through the slot 3a formed at the shadow mask 3 in the slim-type cathode ray tube. Specifically, FIG. 2 shows a case that the electron beam passes through the slot of the shadow mask 3 at a deflection angle of β for the conventional cathode ray tube and another case that the electron beam passes through the slot of the shadow mask 3 at a deflection angle of α for the slim-type cathode ray tube.
In the path along which the electron beam passes through the shadow mask 3 applied to the slim-type cathode ray tube, the electron beam passing through the shadow mask 3 at a deflection angle of α collides with one side of the slot of the shadow mask 3, with the result that interference occurs between the electron beam and the slot of the shadow mask 3.
FIG. 3 is a view showing the shapes of a normal electron beam and a distorted electron beam. When interference occurs between the electron beam and the slot of the shadow mask, the shape of the electron beam is distorted as shown in FIG. 3. This distortion decreases the amount of electron beam arriving at the fluorescent body, which affects brightness of the cathode ray tube.
In order to solve the problem caused by the interference described above, it is necessary to appropriately change the shape of the slot 3a formed at the shadow mask 3. Especially, it is preferable to increase the width of the slot 3a of the shadow mask 3, which prevents interference between the electron beam and the slot of the shadow mask 3.
As the cathode ray tube becomes large and flat, the shadow mask 3 is also formed flat. As a result, the structural strength of the shadow mask 3 is decreased, and therefore, several problems, such as curvature distortion and vibration caused by external impacts and heat distortion, are generated.
When the width of the slot 3a formed at the shadow mask 3 is increased, the structural strength of the shadow mask 3 is further decreased. Consequently, a method of increasing the structural strength of the shadow mask is required.